This joint cooperative study of the Natural History of Congenital Cardiovascular Defects--ventricular septal defect, valvar aortic stenosis, and valvar pulmonary stenosis in their isolated forms--is now in its ninth year. The study has three main objectives: (1) to provide means of validating the hemodynamic status indirectly, i.e., without cardiac catheterization, (2) to provide a basis for evaluating the advisability of surgery in cases where the comparative merits of medical and surgical treatment are currently in doubt and to identify cases where surgery is not warranted; (3) to provide a means of predicting the clinical outlook for any patient with any of the above lesions. Patients were admitted to the study at the time of a diagnostic cardiac catheterization, either retroactively, covering the period from July 1, 1958, to June 30, 1965 with repeat catheterization at the end of eight years, or propsectively, from July 1, 1966, to June 30, 1969, with repeat catheterization at the end of four years. In Feb. 1974 statistical analysis commenced. Sub committees were than formed to commence the non-invasive assessment of aortic stenosis, pulmonary stenosis and ventricular septal defect; the majority of this work being completed. Further subcommittees were than formed and are currently involved in evaluating the clinical course of each of the three major lesions. The work of the different subcommittees is evaluated at the major meetings at which all principal investigators are present. Commencing February 1975, it has been agreed that Dr. A. S. Nadas will devote each morning for a period of six months in compiling in final report of the findings of the Natural History Study. In the meantime, the work of the various subcommittees will continue, with submission of manuscripts for publication as they are completed.